MicroProcessors Lec. 2 Dr. Tamer Samy Gaafar Introduction A computer is a programmable machine that receives input, stores and manipulates data//information, and provides output in a useful format.machinedatainformation A computer is a programmable machine that receives input, stores and manipulates data//information, and provides output in a useful format.machinedatainformation 4 Diagram Of A Computer System Program Word CPU ROMRAMI/O interface I/O devices CPU 6 Basic computer system consist of a Central processing unit (CPU), memory (RAM and ROM), input/output (I/O) unit. Block diagram of a basic computer system Address bus Data busControl bus 1. CPU - Central Processing Unit the portion of a computer system that carries out the instructions of a computer program the primary element carrying out the computer's functions. It is the unit that reads and executes program instructions. The data in the instruction tells the processor what to do. 7 Pentium D dual core processors 2. Memory physical devices used to store data or programs (sequences of instructions) on a temporary or permanent basis for use in an electronic digital computer. Computer main memory comes in two principal varieties: random-access memory (RAM) and read-only memory (ROM). random-access memoryread-only memory RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer's initial start- up instructions. In general, the contents of RAM are erased when the power to the computer is turned off, but ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. BIOSoperating system 8 3. I/O Unit Input/output (I/O), refers to the communication between an information processing system (such as a computer), and the outside world possibly a human, or another information processing system.information processing systemcomputer Inputs are the signals or data received by the system, and outputs are the signals or data sent from it Inputs outputs Devices that provide input or output to the computer are called peripheralsperipherals On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O.personal computermousedisplayprinterHard disk drivesfloppy disk drivesoptical disc drivesComputer networking 9 10 Nibble4 bit Byte8 bit Word16 bit Long word32 bit 11 Block diagram of a Microprocessor Fetching Cycles The fetch cycle takes the instruction required from memory, stores it in the instruction register, and moves the program counter on one so that it points to the next instruction. Execute cycle The actual actions which occur during the execute cycle of an instruction. depend on both the instruction itself and the addressing mode specified to be used to access the data that may be required. 13 Step 1 14 Instruction pointer (program counter) hold the address of the next instruction to be fetch. Step 2 15 FETCHING AN INSTRUCTION (cont.) Step 3 16 FETCHING AN INSTRUCTION (cont.) Step 4 17 FETCHING AN INSTRUCTION (cont.) Step 5 18 FETCHING AN INSTRUCTION (cont.) Step 6 19 FETCHING AN INSTRUCTION (cont.) 1. Load A 2. Add D 3. Sub E, R0 4. Mul B, C 1- (pc) > MAR, Read 2- MM (MAR) > MBR pc > pc 3- (MBR) > IR 4- Address field of IR > MAR, Read 5- MM (MAR) > MBR 6- (MBR) > Acc 7- END Fetch Execut e 1- (pc) > MAR, Read 2- MM (MAR) > MBR pc > pc 3- (MBR) > IR 4- Address field of IR > MAR, Read 5- MM (MAR) > MBR 6- (MBR) > ALU (i/p #1) 7- (ACC) > ALU (i/p #2) Add 8- END Fetch Execute 1- (pc) > MAR, Read 2- MM (MAR) > MBR pc > pc 3- (MBR) > IR 4- Address field of IR > MAR, Read 5- MM (MAR) > MBR 6- (MBR) > ALU (i/p #1) 7- (R0) > ALU (i/p #2) SUB 8- END Fetch Execute ALURegister Section Control and timing section Address bus Data bus Control bus 24 Block diagram of a microprocessor The component that performs the arithmetic and logical operations the most important components in a microprocessor, and is typically the part of the processor that is designed first. able to perform the basic logical operations (AND, OR), including the addition operation. The inclusion of inverters on the inputs enables the same ALU hardware to perform the subtraction operation (adding an inverted operand), and the operations NAND and NOR. 25 2 bits of ALU4 bits of ALU 26 The circuitry that controls the flow of information through the processor, and coordinates the activities of the other units within it. In a way, it is the "brain within the brain", as it controls what happens inside the processor, which in turn controls the rest of the PC. On a regular processor, the control unit performs the tasks of fetching, decoding, managing execution and then storing results. 27 28 The register section/array consists completely of circuitry used to temporarily store data or program codes until they are sent to the ALU or to the control section or to memory. The number of registers are different for any particular CPU and the more register a CPU have will result in easier programming tasks. Registers are normally measured by the number of bits they can hold, for example, an "8-bit register" or a "32-bit register".bits8-bit32-bit 29 30 a register in which intermediate arithmetic and logic results are stored. example for accumulator use is summing a list of numbers. The accumulator is initially set to zero, then each number in turn is added to the value in the accumulator. Only when all numbers have been added is the result held in the accumulator written to main memory or to another, non-accumulator, CPU register. 31 an 8 bit register used to store the status of CPU, such as carry, zero, overflow and half carry. 32 FlagNameDescription ZZero flag Indicates that the result of a mathematical or logical operation was zero. CCarry flag Indicates that the result of an operation produced an answer greater than the number of available bits. (This flag may also be set before a mathematical operation as an extra operand to certain instructions, e.g. "add with carry".) XExtend flag Masks the XIRQ request when set. It is set by the hardware and cleared by the software as well is set by unmaskable XIRQ. NNegative/ Sign flag Indicates that the result of a mathematical operation is negative. In some processors, the N and S flags have different meanings: the S flag indicates whether a subtraction or addition has taken place, whereas the N flag indicates whether the last operation result is positive or negative. VOverflow Flag Indicates that the result of an operation has overflowed according to the CPU's word representation, similar to the carry flag but for signed operations. Iinterrupts Interrupts can be enabled or disabled by respectively setting or clearing this flag. Modifying this flag may be restricted to programs executing in supervisor mode 33 a 16 bit register, used to store the next address of the operation code to be fetched by the CPU. Not much use in programming, but as an indicator to user only. Purpose of PC in a Microprocessor to store address of tos (top of stack) to store address of next instruction to be executed. count the number of instructions. to store base address of the stack. 34 The stack is configured as a data structure that grows downward from high memory to low memory. At any given time, the SP holds the 16- bit address of the next free location in the stack. The stack acts like any other stack when there is a subroutine call or on an interrupt. ie. pushing the return address on a jump, and retrieving it after the operation is complete to come back to its original location. 35 a subsystem that transfers data between computer components inside a computer or between computers. 4 PCI Express bus card slots (from top to bottom: x4, x16, x1 and x16), compared to a traditional 32-bit PCI bus card slot (very bottom). 36 37 The data bus is 'bi-directional' data or instruction codes from memory or input/output.are transferred into the microprocessor the result of an operation or computation is sent out from the microprocessor to the memory or input/output. Depending on the particular microprocessor, the data bus can handle 8 bit or 16 bit data. 38 The address bus is 'unidirectional', over which the microprocessor sends an address code to the memory or input/output. The size (width) of the address bus is specified by the number of bits it can handle. The more bits there are in the address bus, the more memory locations a microprocessor can access. A 16 bit address bus is capable of addressing 65,536 (64K) addresses. 39 The control bus is used by the microprocessor to send out or receive timing and control signals in order to coordinate and regulate its operation and to communicate with other devices, i.e. memory or input/output. 40 Also called clock rate, the speed at which a microprocessor executes instructions. Every computer contains an internal clock that regulates the rate at which instructions are executed and synchronizes all the various computer components. 41 Intel 8085 Intel 8086 Motorola The 8086 is a 16-bit microprocessor chip designed by Intel, which gave rise to the x86 architecture; development work on the 8086 design started in the spring of 1976 and the chip was introduced to the market in the summer of The Intel 8088, released in 1979, was a slightly modified chip with an external 8-bit data bus (allowing the use of cheaper and fewer supporting logic chips and is notable as the processor used in the original IBM PC. 43 The Intel 8085 is an 8-bit microprocessor introduced by Intel in It was binary-compatible with the more-famous Intel 8080 but required less supporting hardware, thus allowing simpler and less expensive microcomputer systems to be built. An Intel 8085AH processor. Produced From 1977 to 1990s Common manufacturer(s) Intel and several others Max. CPU clock rateCPUclock rate 3,5 and 6 MHz Instruction setpre x86x86 Package(s) 40 pin DIPDIP 44 Text book p.16 p.55